Oroville Dam: Final concrete slab placed on rebuilt spillway

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Overview of the Lake Oroville main spillway during Phase 2 of the recovery effort.

Workers from Kiewit Infrastructure place concrete on the last remaining slab on the upper chute of the Lake Oroville main spillway during Phase 2 of the recovery efforts at the Butte County, California site. October 11, 2018.
(Florence Low / California Department of Water Resources)

A night shift crew continues with concrete placement for one of the last sidewalls on the upper chute of the Lake Oroville main spillway in Butte County, California. Photo taken October 12, 2018.
(Kelly M. Grow / California Department of Water Resources)

Workers from Kiewit Infrastructure place concrete for the last sidewall on the lower chute of the Lake Oroville main spillway during Phase 2 of the recovery effort at the Butte County, California site. Photo taken October 15, 2018.
(Ken James / California Department of Water Resources)

Workers from Kiewit Infrastructure backfill and raise the area around the underdrain piping system outside the sidewalls on the upper chute of the Lake Oroville main spillway in Butte County, California. Photo taken October 15, 2018.
(Ken James / California Department of Water Resources)

Construction personnel gather below as workers from Kiewit Infrastructure place concrete for the last sidewall on the upper chute of the Lake Oroville main spillway during Phase 2 of the recovery effort at the Butte County, California site. Photo taken October 18, 2018.
(Kelly M. Grow / California Department of Water Resources)

José Mercado, of Kiewit Infrastructure, secures ties on the last rebar panel before concrete was poured into the sidewall on the upper chute of the Lake Oroville main spillway during Phase 2 of the recovery effort at the Butte County, California site. Photo taken October 18, 2018.
(Kelly M. Grow / California Department of Water Resources)

Nicholas Thomlinson, of Kiewit Infrastructure, drags a screed across the top of fresh concrete placed for the last sidewall on the upper chute of the Lake Oroville main spillway during Phase 2 of the recovery effort at the Butte County, California site. Photo taken October 18, 2018.
(Kelly M. Grow / California Department of Water Resources)

As the sun sets, Juan Ramon Garcia, of Kiewit Infrastructure, finishes the final pass of roller-compacted concrete on the Lake Oroville emergency spillway splashpad. The section was placed up against the spillway weir during Phase 2 of the recovery effort at the Butte County, California site. October 22, 2018.
(Kelly M. Grow / California Department of Water Resources)

A worker from Kiewit Infrastructure sprays compressed air to clean small debris off the middle chute of the Lake Oroville main spillway in Butte County, California. Photo taken October 24, 2018.
(Kelly M. Grow / California Department of Water Resources)

Workers from Kiewit Infrastructure backfill and raise the area around the underdrain piping system outside the sidewalls on the upper chute of the Lake Oroville main spillway in Butte County, California. October 27, 2018.
(Florence Low / California Department of Water Resources)

A drone provides an overview of the recently completed Lake Oroville main spillway during Phase 2 of the recovery effort at the Butte County, California site. Photo taken October 29, 2018.
(Ken James / California Department of Water Resources)

Aerial photo of the recently completed Lake Oroville main spillway during Phase 2 of the recovery effort at the Butte County, California site. Photo taken October 29, 2018.
(Ken James / California Department of Water Resources)

OROVILLE — The state Department of Water Resources announced Wednesday that it met its self-set Nov. 1 deadline to finish placing concrete on the entirely rebuilt Oroville Dam spillway.

The department does not plan to use the spillway for at least one month as concrete continues to cure, but representatives say the structure is back to its original design capacity and could pass flows of up to 270,000 cubic-feet per second if needed.

The nation’s tallest dam made national headlines in February 2017 when its main spillway split open and the emergency spillway, which then consisted of only a concrete weir with an unlined hillside below, was used for the first time in history. At least 188,000 downstream residents were ordered to evacuate immediately.

Though the worst fears were not realized and everyone was soon able to return home, the incident negatively impacted local tourism, recreation and community trust in the structure and its operators in a way that is still felt. It shook the dam industry and prompted dam owners to take a closer look at other aging facilities.

Now the end of reconstruction is in sight with the main spillway ready to use and the emergency spillway expected to be complete in early 2019. The department is targeting midsummer 2019 for reopening the road over the dam and the spillway boat launch facility.

Observers may still see crews on the main spillway for some time, as there is still joint sealing, dry finishing and site cleanup work to be done.

A new concrete surface can be seen Tuesday on the energy-dissipating dentates at the bottom of the main Oroville Dam spillway. The structures were beaten up by concrete washing down the chute when the spillway broke up in February 2017.

The department said concrete placement on the spillway was finished ahead of the deadline, with the dentates or energy dissipators done by Oct. 20, the final concrete wall placed on Oct. 18 and the last concrete slab placed on the spillway chute on Oct. 11. A total of 612 new erosion-resistant concrete slabs were installed in phases one and two, according to DWR.

Kiewit Infrastructure West Co., the lead contractor on the Oroville recovery project, started literally from the ground up, placing reinforced structural concrete at the bottom of the spillway and temporary roller-compacted concrete, or RCC, in the middle, while patching the uppermost 730 feet, in time for the Nov. 1 deadline in 2017.

For the second phase of construction, the middle and upper chutes and walls and energy dissipators at the bottom of the spillway were filled with reinforced structural concrete. Work continues over at the emergency spillway, where a structural concrete cap is being built to connect the new roller-compacted concrete buttress to the emergency spillway weir.

Kiewit’s contract will expire at the end of January, though Project Director Jeff Petersen said it may be extended for grading work to get the spillway hillside as close as possible to its original condition.

Although the replacement of the main Oroville Dam spillway is considered complete, on Tuesday there were still a number of people at work in the concrete chute.

Department representatives said in Wednesday’s media call that work on the emergency spillway was ahead of schedule. New features there, including a concrete buttress and “splash pad,” have been added to prevent the dangerous type of erosion that led to the evacuation orders in February 2017, should the emergency spillway ever be used again.

Crews finished the expansive splash pad on Friday, consisting of 700,000 cubic feet of RCC. Work on the buttress which is also made of RCC at the base of the emergency spillway wrapped up earlier in October.

The ad hoc group led by Assemblyman James Gallagher, R-Yuba City, Sen. Jim Nielsen, R-Red Bluff, and a DWR representative met for the second time on Tuesday to discuss the Oroville Dam comprehensive needs assessment.

Infrastructure changes are being considered in the assessment, which is slated to be complete by the end of 2019. Nielsen and Gallagher appointed 12 community members to the committee.

Gallagher said on Wednesday that he advocated for leaving more space in the reservoir, especially during winter months, while DWR works to get the water control operations manual updated with the U.S. Army Corps of Engineers. The department finalized an operations plan for the 2018-2019 flood season that calls for lower than average lake levels this winter.

Crews Tuesday work on backfilling the side walls of the main Oroville Dam spillway.

Gallagher said the committee requested that DWR include recreational impacts of any changes considered in the assessment.

DWR also gave a presentation about the vegetation known as the “green spot” on the face of the dam, which Gallagher said “helped dissuade concerns about a piping issue.” The assemblyman said there was also a discussion about the spillway gates, which the department has been monitoring closely.

Tests have shown them to be stable, but the department will continue to assess whether the gates need to be repaired or even replaced, he said. Gallagher said he is focused on long-term changes to the facility and its operations.

“I do feel confident that once this is done we’re definitely going to have a much better, stronger spillway, the spillway we always should have had,” he said.

A recording of the meeting has not been posted online yet. The meetings are closed to media.

Another case management conference is scheduled for Friday for several lawsuits pending against DWR over the spillway crisis. Parties suing the department run the gamut from farmers and business owners to the city of Oroville and the South Feather Water and Power Agency.

Risa Johnson covers local politics in Butte County and the City of Oroville for the Chico Enterprise-Record and Oroville Mercury-Register newspapers. Since February 2017, she has written extensively about the Oroville Dam crisis. She is a proud alumna of Chico State University.